How to increase the "Strength" of a normal map procedurally, Before the "Normal Map" node?
You can separate the RGB channels, amplify them with a Map Range node (say, 0.4 to 0.6 mapped to 0, 1), and then recombine them.
However, amplifying normal maps like this should never be neccesary. Normal maps do not alter geometry, unless it is not being used for normals: in the case that Cycles is using them to displace the existing vertices through a displacement material output. Changing the normals of a mesh will never change the mesh itself. I think you are mistaking for weak normal maps what is actually an inherent disability in faking light interactions.